1. Field of the Invention
The present invention is directed to an image forming apparatus. More particularly, the present invention is related to an image forming apparatus having a cooling unit for cooling an intermediate transfer medium.
2. Description of the Related Art
Generally, an electrophotographic image forming apparatus develops a predetermined electrostatic latent image formed on a photosensitive medium into a visible image, and then transfers the visible image onto a printing paper. More particularly, a wet electrophotographic image forming apparatus transfers and superposes each of a plurality of visible images formed on a plurality of photosensitive media onto an intermediate transfer medium to form a full color image, and then transfers the full color image onto the printing paper. The intermediate transfer medium may include an intermediate transfer belt, intermediate transfer drum, and so on. The image transferred onto the printing paper from either of the photosensitive media and the intermediate transfer medium is fixed thereon by high temperature and high pressure to keep the image in a transferred shape. To keep a life span or a performance of the photosensitive medium, there is a need to prevent heat of a fusing unit from heating the photosensitive medium over a predetermined temperature.
FIG. 1 shows an example of a conventional wet electrophotographic image forming apparatus having an intermediate transfer drum. The image forming apparatus cools a photosensitive medium to prevent the photosensitive medium from being heated over a predetermined temperature.
Referring to FIG. 1, the image forming apparatus includes an intermediate transfer medium 10, a photosensitive medium 20, a developing roller 30, and an ink supply unit 40.
The intermediate transfer medium 10 is drum-shaped and disposed to be in contact with the photosensitive medium 20. It transfers the image transferred from the photosensitive medium 20 onto a printing paper P.
The photosensitive medium 20 is drum-shaped and disposed to be in contact with the intermediate transfer medium 10. A used-ink cleaner 21, a charge eliminating unit 22, and a charging unit 23 are disposed on an outer circumference of the photosensitive medium 20 in a rotating direction thereof from a place where the photosensitive medium 20 is in contact with the intermediate transfer medium 10.
The developing roller 30 is disposed to be in contact with the photosensitive medium 20 in front of the charging unit 23 in a rotating direction of the photosensitive medium 20. It develops the electrostatic latent image formed on the photosensitive medium 20 into a visible image with ink being supplied by the ink supply unit 40.
There is an exposed space between the charging unit 23 and the developing roller 30. A laser beam scanned by a laser-scanning unit 24 irradiates the photosensitive medium 20 in the exposed space. An ink nozzle 41, which supplies the ink from the ink supply unit 40, is provided between the exposed space and the developing roller 30.
The ink supply unit 40 has a predetermined store of ink and supplies the ink for a nip between the developing roller 30 and the photosensitive medium 20 through the ink nozzle 41. Also, the ink supply unit 40 further includes an ink-cooling part (not shown) to keep the ink at a predetermined temperature.
The operation of the image forming apparatus having the aforementioned structure is explained hereinafter.
When the photosensitive medium 20 rotates according to a printing order, used ink remaining on the photosensitive medium 20 is removed by the used-ink cleaner 21, and a residual charge on a surface of the photosensitive medium 20 is eliminated by the charge eliminating unit 22. The surface of the photosensitive medium 20 is charged by the charging unit 23, and is exposed to a laser beam scanned by the laser-scanning unit 24, thereby forming an electrostatic latent image in a pattern corresponding to a printing data. The photosensitive medium 20 keeps rotating, and the electrostatic latent image is developed into a visible image by the ink supplied by the ink supply unit 40 and the developing roller 30. The visible image formed on the photosensitive medium 20 is transferred onto the intermediate transfer drum 10, which rotates and is in contact with the photosensitive medium 20. The image transferred to the intermediate transfer drum 10 is transferred onto the printing paper P and fixed thereon. The intermediate transfer drum 10 is heated since a predetermined heat is applied to the printing paper P when the image is transferred from the intermediate transfer drum 10 onto the printing paper P and fused thereon. As the intermediate transfer drum 10 is heated, the photosensitive medium 20, which rotates and is in contact with the intermediate transfer drum 10, is heated. When the photosensitive medium 20 is heated over a predetermined temperature, the life span of the photosensitive medium 20 may decrease and performance thereof may deteriorate. However, the photosensitive medium 20 of the image forming apparatus heated by the intermediate transfer drum 10 is cooled by the ink, since the image forming apparatus has the ink supply unit 40 that supplies ink at a predetermined temperature between the photosensitive medium 20 and the developing roller 30. Therefore, the photosensitive medium 20 is kept below a predetermined temperature. However, a method that directly cools the photosensitive medium 20 with the cooling ink repeatedly heats up and cools down the photosensitive medium 20, thereby causing heat fatigue of the photosensitive medium 20. The heat fatigue may shorten the life span thereof.
Also, when the intermediate transfer belt is used as the intermediate transfer medium 10, a front side of the intermediate transfer belt is generally cooled. However, when a coolant directly cools the front side of the intermediate transfer belt, used ink remaining on the intermediate transfer belt after the transfer contaminates the coolant. Therefore, there is a need to periodically change the coolant. Also, when the coolant is not completely removed from the front side of the photosensitive medium belt, a residual coolant thereof can contaminate the ink. Thus, the image transferred from the photosensitive medium to the intermediate transfer belt may be deteriorated.
Accordingly, a need exists for an image forming apparatus that cools an intermediate transfer medium to substantially prevent overheating of a photosensitive medium.